This invention relates to novel compositions comprising a waterglass, to fire resistant glass laminates comprising a waterglass based intumescent interlayer and to methods for the production of such laminates. Fire resistant glass laminates incorporating a waterglass based intumescent interlayer are sold by the Pilkington group of companies under the trade marks PYROSTOP and PYRODUR. These laminates are produced by pouring an aqueous waterglass solution onto the surface of a first glass pane and drying the solution in such a manner that a clear interlayer is formed. A second pane of glass is then placed on top of the first pane to form a laminate. Laminates containing more than two sheets of glass and more than one interlayer are also produced but are relatively thick and correspondingly expensive to produce.
When these laminates are exposed to a fire, the interlayer intumesces and expands to form a foam. The foam assists in preserving the structural integrity of the laminate for a longer period thereby maintaining a barrier to the propagation of the fire. The foam is also an insulator which reduces the amount of heat transmitted through the glazing and thereby inhibits the ignition of flammable material on the non-fire side of the glass.
The production of laminates having a waterglass based interlayer has been described in a number of patents including British Patents GB 1518958, GB 2199535 and United States patents U.S. Pat. No. 4,451,312, 4,626,301 and 5,766,770. The waterglass solutions proposed to be useful are the alkali metal silicates wherein the weight ratio SiO2:M2O (wherein M represents an alkali metal) is in the range 2.5:1 to 5.0:1. The waterglass solutions used in practice in these patents and in the commercially available fire resistant glass laminates are sodium silicates wherein the ratio of SiO2:M2O is 3.4:1 or greater. Sodium silicate waterglasses wherein the ratio SiO2:Na2O is less than 3.3:1 have not been used in practice because they are viscous and thereby difficult to handle and dry to form a brittle interlayer which provides lower fire resistance and less impact resistance when incorporated into a fire resistant glazing.
U.S. Pat. Nos. 4,626,301 and 5,766,770 further disclose the incorporation of a polyhydric organic compound into the waterglass solution. The organic compound serves to reduce the incidence of cracking at the surface of the dried interlayer and in a fire helps maintain a barrier to the fire by binding the char. However since organic compounds are flammable the quantity used has been kept to a minimum in order not to provide a fuel for a fire. U.S. Pat. No. 5,766,770 states that the preferred such polyhydric compound is glycerol and that the interlayer should preferably contain less than 6% by weight of the organic compound.